1. Field of the Invention
This invention relates to both a method and an apparatus for building a forming structure of a cylindrical tire by winding a belt-shaped material on a drum.
2. Background of the Invention
In a tire building industry, a radial tire is built, for instance, as follows. A tread band with belt built cylindrically in advance on another building drum is set on the cylindrical carcass built on a tire building drum. Then, the cylindrical carcass is shaped to be toroidal and the belt tread band and the carcass are joined. In general, such a tread band is built by winding a belt-shaped tread rubber material on the building drum. However, the belt-shaped tread rubber material is disadvantageous in that, since both edge portions, in their widthwise direction, are smaller in thickness than the middle, the edge portions contract longitudinally. This side shrinkage causes a phenomena called "short-side" with the result that the front and rear ends of the tread rubber material are not positively butt-joined.
One example of a conventional building method or apparatus of cylindrical tire-building member has been disclosed, for instance, by Japanese Published Patent Application (OPI) No. 42445/1983. The apparatus includes a chuck mechanism for clamping both edge portions of a rubber sheet. An air cylinder moves the chuck mechanism towards a forming drum. A brake mechanism holds the rear end portion of the rubber sheet and slightly elongates the two edge portions of the rubber sheet in cooperation with the chuck mechanism. Finally, a depressing mechanism presses the front end portion of the rubber sheet against the drum. In the apparatus after the two edge portions of the front end portion of the rubber sheet have been clamped by the chuck mechanism, the chuck mechanism is moved towards the drum by the air cylinder. In this operation, while the chuck mechanism moves a predetermined distance, the brake mechanism holds the rear end portion of the rubber sheet to slightly elongate the two edge portions of the rubber sheet to slightly elongate the "short-side". Thereafter, the front end of the rubber sheet is moved to a predetermined position above the drum by the chuck mechanism and is then pressed against the drum by the depressing mechanism. Under this condition, the chuck mechanism is moved away from the rubber sheet. While the rubber sheet is being fed, the drum is rotated, to form the cylindrical tire forming member.
In the above-described apparatus or method, while the rear end of the rubber sheet is being held by the brake system, the chuck mechanism holding the two edge portions of the front end portion of the rubber sheet is moved so that the two edge portions of the rubber sheet are slightly elongated. Therefore, in this operation, the central portion in the widthwise direction, of the rubber sheet is also somewhat elongated. As a result, the front and rear ends of the rubber sheet may be not satisfactorily butt-joined. Furthermore, in the conventional apparatus or method, after the front end of the rubber sheet has been pressed against the drum, the chuck mechanism is moved away from the rubber sheet without maintaining the two edge portions of the rubber sheet elongated. Therefore, the two edge portions of the rubber sheet are partially elastically deformed, i.e., contracted, thus causing the unsatisfactory joint.